A plasma display device has recently been drawing attention among the flat panel display technologies. Compared to a liquid crystal display (LCD) panel, a plasma display panel can provide a higher display speed, a larger field of view, easier upsizing in manufacturing, and higher display quality due to its self-emitting characteristic.
To display color images, a plasma display device generally produces ultraviolet rays through gas discharging for exciting phosphors. In the structure of the device, dividing walls partition a discharge space in the panel into a plurality of discharge cells each of which has a phosphor layer.
The plasma display device falls roughly into an alternating current (AC) plasma display device and a direct current (DC) plasma display device according to its operation principle. Also, the plasma display device is divided into a surface discharge type and an opposing discharge type according to configuration of electrodes. In terms of providing high resolution, easy upsizing, and simple manufacturing, today's mainstream is a surface discharge type plasma display device with a three-electrode structure. To be more specific, the device has two substrates opposing each other. One of the substrates has pairs of display electrodes formed of scan electrodes and sustain electrodes arranged in parallel with each other; and the other substrate has address electrodes disposed so as to be orthogonal to the display electrodes on the opposing substrate, dividing walls, and phosphor layers. The aforementioned structure allows the phosphor layer to be relatively thick, providing high quality in color display using phosphors.
Now will be described the structure of a plasma display panel of a plasma display device with reference to FIG. 7. On front-side substrate 1, which is made of glass or other transparent materials, a plurality of pairs of display electrodes 2 formed of scan electrodes and sustain electrodes is arranged in a stripe shape, as shown in FIG. 7. Dielectric layer 3 is disposed so as to cover an array of the electrodes, and over which, protecting film 4 is formed.
On the other hand, on the rear-side substrate 5 facing substrate 1 disposed on the front side, address electrodes 7 are formed into stripes and arranged so as to be orthogonal to display electrodes 2 on substrate 1. Overcoat layer 6 covers the stripes of address electrodes 7. On overcoat layer 6 between address electrodes 7, a plurality of dividing walls 8 is disposed in parallel with the rows of address electrodes 7. Furthermore, phosphor layer 9 is formed between dividing walls 8 and on the surface of overcoat layer 6.
Substrates 1 and 5 are located, via a tiny discharge space, in an opposing arrangement so that display electrodes 2 formed of the scan electrodes and sustain electrodes are generally orthogonal to address electrodes 7, and the opposing sides of the two substrates are sealed with each other. The discharge space formed between substrates 1 and 5 is filled with discharge gas—the gas may be any one of Helium, Neon, Argon, Xenon, or mixture of them. Dividing wall 8 divides the discharge space into a plurality of cells, that is, a plurality of discharge cells are formed at intersections of display electrodes 2 and address electrodes 7. Phosphor layer 9 is disposed one by one in each cell so as to have a successive order of the red, green, and blue phosphors.
FIG. 8 shows an arrangement of the electrodes disposed on a plasma display panel. The pairs of the scan electrodes and the sustain electrodes, and the address electrodes are, as shown in FIG. 8, arranged into a matrix with M (rows) by N (columns); the structure has M scan electrodes (SCN1–SCNM) and M sustain electrodes (SUS1–SUSM) in the row directions of the matrix, on the other hand, has N address electrodes (D1–DN) in the column directions of the matrix (see Japanese Patent Laid-Open Application No. 2000-47636).
When an image is displayed on such a plasma display panel, first, a voltage pulse (writing pulse) is applied between the address electrode and the scan electrode defining the selected cell for address discharge. Then, a sustaining pulse having a periodic phase-reverse is applied between the scan electrode and the sustain electrode for sustain discharge.
Terminal lead-out sections of the sustain electrodes are divided into plural connection blocks according to the number of terminals disposed on one flexible printed circuit (hereinafter referred as an FPC). Each lead-out section of the sustain electrodes connects with an FPC at each connection block.
When the waveform for driving the sustain electrodes has a fixed form, a solid pattern is provided on the copper foil section of each FPC to avoid waveform distortion due to undesired impedance and inductance.
In the plasma display device structured above, however, variations in the current flow into the FPCs for driving the sustain electrodes have caused a problem. Now, suppose that a plasma display panel has a structure in which evenly divided sustain electrodes in the discharge area are connected with 6FPCs. When the panel displays an image—suppose that the uppermost one-twelfth of the effective display area of the panel is colored in black, and the rest of the area is in white. In this case, the FPC located in the uppermost section of the panel has a small current flow and therefore the loss in driving waveform voltage decreases at the section. This increases practical voltage to the discharge cell corresponding to the uppermost FPC, that is, the uppermost section has higher luminance than other cells in the panel. As described above, the inconsistencies in luminance have been a problem in the prior-art structure.